Bulk sodium species treatment of thin film photovoltaic cell and manufacturing method

ABSTRACT

A method for forming a thin film photovoltaic device is provided. The method includes providing a transparent substrate comprising a surface region. A first electrode layer is formed overlying the surface region. A chalcopyrite material is formed overlying the first electrode layer. In a specific embodiment, the chalcopyrite material comprises a copper poor copper indium disulfide region. The copper poor copper indium disulfide region having an atomic ratio of Cu:In of about 0.95 and less. The method includes compensating the copper poor copper indium disulfide region using a sodium species to cause the chalcopyrite material to change from an n-type characteristic to a p-type characteristic. The method includes forming a window layer overlying the chalcopyrite material and forming a second electrode layer overlying the window layer.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 12/563,065, filed Sep. 18, 2009, which claimspriority to U.S. Provisional Patent Application No. 61/101,113, filedSep. 29, 2008, entitled “BULK SODIUM SPECIES TREATMENT OF THIN FILMPHOTOVOLTAIC CELL AND MANUFACTURING METHOD” by inventor HOWARD W. H.LEE, the disclosures of both the applications are incorporated byreference herein in their entirety for all purposes.

This application is related to U.S. Provisional Patent Application No.61/100,854, filed Sep. 29, 2008, and U.S. patent application Ser. No.12/563,064 filed Sep. 18, 2009, which are incorporated by reference forall purpose herein.

BACKGROUND OF THE INVENTION

The present invention relates generally to photovoltaic materials andmanufacturing method. More particularly, the present invention providesa method and structure for manufacture of high efficiency thin filmphotovoltaic cells. Merely by way of example, the present method andmaterials include absorber materials made of copper indium disulfidespecies, copper tin sulfide, iron disulfide, or others for singlejunction cells or multi junction cells.

From the beginning of time, mankind has been challenged to find way ofharnessing energy. Energy comes in the forms such as petrochemical,hydroelectric, nuclear, wind, biomass, solar, and more primitive formssuch as wood and coal. Over the past century, modern civilization hasrelied upon petrochemical energy as an important energy source.Petrochemical energy includes gas and oil. Gas includes lighter formssuch as butane and propane, commonly used to heat homes and serve asfuel for cooking Gas also includes gasoline, diesel, and jet fuel,commonly used for transportation purposes. Heavier forms ofpetrochemicals can also be used to heat homes in some places.Unfortunately, the supply of petrochemical fuel is limited andessentially fixed based upon the amount available on the planet Earth.Additionally, as more people use petroleum products in growing amounts,it is rapidly becoming a scarce resource, which will eventually becomedepleted over time.

More recently, environmentally clean and renewable sources of energyhave been desired. An example of a clean source of energy ishydroelectric power. Hydroelectric power is derived from electricgenerators driven by the flow of water produced by dams such as theHoover Dam in Nevada. The electric power generated is used to power alarge portion of the city of Los Angeles in California. Clean andrenewable sources of energy also include wind, waves, biomass, and thelike. That is, windmills convert wind energy into more useful forms ofenergy such as electricity. Still other types of clean energy includesolar energy. Specific details of solar energy can be found throughoutthe present background and more particularly below.

Solar energy technology generally converts electromagnetic radiationfrom the sun to other useful forms of energy. These other forms ofenergy include thermal energy and electrical power. For electrical powerapplications, solar cells are often used. Although solar energy isenvironmentally clean and has been successful to a point, manylimitations remain to be resolved before it becomes widely usedthroughout the world. As an example, one type of solar cell usescrystalline materials, which are derived from semiconductor materialingots. These crystalline materials can be used to fabricateoptoelectronic devices that include photovoltaic and photodiode devicesthat convert electromagnetic radiation into electrical power. However,crystalline materials are often costly and difficult to make on a largescale. Additionally, devices made from such crystalline materials oftenhave low energy conversion efficiencies. Other types of solar cells use“thin film” technology to form a thin film of photosensitive material tobe used to convert electromagnetic radiation into electrical power.Similar limitations exist with the use of thin film technology in makingsolar cells. That is, efficiencies are often poor. Additionally, filmreliability is often poor and cannot be used for extensive periods oftime in conventional environmental applications. Often, thin films aredifficult to mechanically integrate with each other. These and otherlimitations of these conventional technologies can be found throughoutthe present specification and more particularly below.

From the above, it is seen that improved techniques for manufacturingphotovoltaic materials and resulting devices are desired.

BRIEF SUMMARY OF THE INVENTION

According to embodiments of the present invention, a method and astructure for forming thin film semiconductor materials for photovoltaicapplications are provided. More particularly, the present inventionprovides a method and structure for forming semiconductor materials usedfor the manufacture of high efficiency photovoltaic cells. Merely by wayof example, the present method and materials include absorber materialsmade of copper indium disulfide species, copper tin sulfide, irondisulfide, or others for single junction cells or multi-junction cells.

In a specific embodiment, a method for forming a thin film photovoltaicdevice is provided. The method includes providing a transparentsubstrate comprising a surface region. A first electrode layer is formedoverlying the surface region. The method includes forming a copper layeroverlying the first electrode layer and forming an indium layeroverlying the copper layer to form a multi-layered structure. In aspecific embodiment, the method includes subjecting at least themulti-layered structure to a thermal treatment process in an environmentcontaining a sulfur bearing species. The method forms a bulk copperindium disulfide material from at least the thermal treatment process ofthe multi-layered structure. In a specific embodiment, the bulk copperindium disulfide material comprising a copper-to-indium atomic ratioranging from about 1.2:1 to about 2:1 and a thickness of a substantiallycopper sulfide material having a copper sulfide surface region. Themethod includes removing the thickness of the copper sulfide material toexpose a surface region having a copper poor surface. The copper poorsurface comprises a copper to indium atomic ratio of less than about0.95:1. The method subjects the copper poor surface and one or moreportions of the bulk copper indium disulfide material to a sodiumspecies to convert the copper poor surface from an n-type semiconductorcharacteristic to a p-type semiconductor characteristic and to convertany of the one or more portions of the bulk copper indium disulfidematerial having the copper-to-indium atomic ratio of less than about0.95:1 from a p-type characteristics to an n-type characteristics. Themethod further subjects the copper poor surface to a treatment processduring a time period associated with the subjecting of the copper poorsurface with the sodium species. A window layer is formed overlying thecopper indium disulfide material.

In an alternative embodiment, a method for forming a thin filmphotovoltaic device is provided. The method includes providing atransparent substrate comprising a surface region. A first electrodelayer is formed overlying the surface region. In a specific embodiment,the method forms a copper indium material comprising an atomic ratio ofCu:In ranging from about 1.35:1 to about 1.60:1 by at least sputtering atarget comprising an indium copper material. The method subjects thecopper indium material to a first thermal treatment process in anenvironment containing a sulfur bearing species to form a copper indiumdisulfide material from at least the first thermal treatment process ofthe copper indium material in a specific embodiment. In a specificembodiment, a copper poor copper indium disulfide material is formedwithin a portion of the copper indium disulfide material. The copperpoor copper indium disulfide material has an atomic ration of Cu:In ofabout 0.99 and less. In a specific embodiment, the method includescompensating the copper poor copper indium disulfide material using asodium species to change in characteristic from an n-type to a p-type.The method further forms a window layer overlying the copper indiumdisulfide material.

In a yet alternative embodiment, a method for forming a thin filmphotovoltaic device is provided. The method includes providing atransparent substrate comprising a surface region. A first electrodelayer is formed overlying the surface region The method includes forminga chalcopyrite material overlying the electrode layer. In a specificembodiment, the chalcopyrite material comprises at least a copper poorcopper indium disulfide material. The copper poor copper indiumdisulfide material includes a copper poor copper indium disulfidematerial surface. The copper poor copper indium disulfide surface has anatomic ratio of Cu:In of about 0.99 and less in a specific embodiment.The method includes compensating the copper poor copper indium disulfidematerial using a sodium species to change in the copper poor copperindium disulfide material from an n-type semiconductor characteristic ap-type semiconductor characteristic in a specific embodiment. The methodforms a window layer overlying the chalcopyrite material and forms asecond electrode layer overlying the window layer.

In a still yet alternative embodiment, a thin film photovoltaic deviceis provided. The thin film photovoltaic device includes a substrate. Thesubstrate includes a surface region. A first electrode layer overliesthe surface region. A chalcopyrite material overlies the first electrodelayer. In a specific embodiment, the thin film photovoltaic deviceincludes a copper poor copper indium disulfide bulk region and a surfaceregion. The copper poor copper indium disulfide bulk region has anatomic ratio of Cu:In of about 0.99 and less. The thin film photovoltaicdevice includes a compensating sodium species provided within one ormore portions of the copper poor copper indium disulfide region tochange the copper poor copper indium disulfide region from an n-typesemiconductor characteristic to a p-type semiconductor characteristic ina specific embodiment. The semiconductor includes a window layeroverlying the copper indium disulfide material and a second electrodelayer overlying the window layer.

Many benefits are achieved by ways of present invention. For example,the present invention uses starting materials that are commerciallyavailable to form a thin film of semiconductor bearing materialoverlying a suitable substrate member. The thin film of semiconductorbearing material can be further processed to form a semiconductor thinfilm material of desired characteristics, such as atomic stoichiometry,impurity concentration, carrier concentration, doping, and others. In aspecific embodiment, the band gap of the resulting copper indiumdisulfide material is about 1.55 eV. Additionally, the present methoduses environmentally friendly materials that are relatively less toxicthan other thin-film photovoltaic materials. In a preferred embodiment,the present method and resulting structure is substantially free from aparasitic junction on an absorber layer based upon a copper poorchalcopyrite material. Also in a preferred embodiment, the open circuitvoltage of the chalcopyrite material such as copper indium disulfideranges from about 0.8 volts and greater and preferably 0.9 volts andgreater or 1.0 volts and greater up to 1.2 volts. Depending on theembodiment, one or more of the benefits can be achieved. These and otherbenefits will be described in more detailed throughout the presentspecification and particularly below.

Merely by way of example, the present method and materials includeabsorber materials made of copper indium disulfide species, copper tinsulfide, iron disulfide, or others for single junction cells or multijunction cells.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-8 are simplified schematic diagrams illustrating a method andstructure for forming a thin film photovoltaic device according to anembodiment of the present invention; and

FIGS. 9-12 are simplified diagrams illustrating a method and structurefor forming a thin film photovoltaic device including sodium speciestreatment according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

According to embodiments of the present invention, a method and astructure for forming semiconductor materials for photovoltaicapplications are provided. More particularly, the present inventionprovides a method for manufacturing thin film photovoltaic devices.Merely by way of example, the method has been used to provide a copperindium disulfide thin film material for high efficiency solar cellapplication. But it would be recognized that the present invention has amuch broader range of applicability, for example, embodiments of thepresent invention may be used to form other semiconducting thin films ormultilayers comprising iron sulfide, cadmium sulfide, zinc selenide, andothers, and metal oxides such as zinc oxide, iron oxide, copper oxide,and others.

FIG. 1-8 are simplified schematic diagrams illustrating a method forforming a thin film photovoltaic device according to an embodiment ofthe present invention. These diagrams are merely examples, which shouldnot unduly limit the claims herein. One skilled in the art wouldrecognize other variations, modifications, and alternatives. As shown inFIG. 1, a substrate 110 is provided. In an embodiment, the substrate 110includes a surface region 112 and is held in a process stage within aprocess chamber (not shown). In another embodiment, the substrate 110 isan optically transparent solid material. For example, substrate 110 canuse material such as glass, quartz, fused silica, or plastic, or metal,or foil, or semiconductor, or composite materials. Depending upon theembodiment, the substrate can be a single material, multiple materials,which are layered, composites, or stacked, including combinations ofthese, and the like. Of course there can be other variations,modifications, and alternatives.

As shown in FIG. 2, the present method forms an electrode layer 120overlying a surface region 112 of substrate 110. The electrode layer canbe a suitable metal material, a semiconductor material or a transparentconducting oxide material, or a combination. Electrode layer 120 can beformed using techniques such as sputtering, evaporation (e.g., usingelectron beam), electro-plating, or a combination of these, and thelike, according to a specific embodiment. Preferably, the electrodelayer is characterized by a resistivity of about 10 Ohm/cm² to 100Ohm/cm² and less according to a specific embodiment. In a specificembodiment, the electrode layer can be made of molybdenum or tungsten.The electrode layer can have a thickness ranging from about 100 nm to 2micron in a specific embodiment, but can also be others depending on theapplication. Other suitable materials such as copper, chromium,aluminum, nickel, or platinum, and the like may also be used. Of course,there can be other variations, modifications, and alternatives.

As shown in FIG. 3, a copper layer 130 is formed overlying the electrodelayer. In particular, copper (Cu) layer 130 is formed overlying theelectrode layer 120. For example, the copper layer can be formed using asputtering process using a suitable copper target. In one example, a DCmagnetron sputtering process can be used to deposit Cu layer 130 ontothe electrode layer 120. The sputtering process is performed under asuitable pressure and temperature. In a specific embodiment, thesputtering process can be performed under a deposition pressure of about6.2 mTorr. In a specific embodiment, the deposition pressure may becontrolled using Ar gas. In a specific embodiment, an Ar gas flow rateof about 32 sccm is used to achieve the desired deposition pressure.Deposition can be provided at room temperature without heating thesubstrate. Of course, minor heating may result due to plasma generatedduring deposition. Additionally, a DC power supply of about 115 W may beused for the sputtering process. Depending on the embodiment, DC powerranging from 100 W to 150 W may be used depending on the specificmaterials used. A deposition time for a Cu layer of 330 nm thickness isabout 6 minutes or more under the described deposition condition. Ofcourse, the deposition condition can be varied and modified according toa specific embodiment.

In a preferred embodiment, the method includes forming a barrier layer125 overlying the electrode layer to form an interface region betweenthe electrode layer and the copper layer. In a specific embodiment, theinterface region is maintained substantially free from a metal disulfidelayer having a semiconductor characteristic that is different from acopper indium disulfide material formed during later processing steps.Depending upon the embodiment, the barrier layer has suitable conductivecharacteristics and can be reflective to allow electromagnetic radiationto reflect back into a photovoltaic cell or can also be transparent orthe like. In a specific embodiment, the barrier layer is selected fromplatinum, titanium, chromium, or silver. Of course, there can be othervariations, modifications, and alternatives.

Referring now to FIG. 4. The method forms an indium layer 140 overlyingcopper layer 130. The indium layer is deposited over the copper layerusing a sputtering process in a specific embodiment. In a specificembodiment, the indium layer can be deposited using a DC magnetronsputtering process under a similar condition for depositing the Culayer. The deposition time for the indium layer may be shorter than thatfor Cu layer. As merely an example, 2 minutes and 45 seconds may beenough for depositing an In layer of about 410 nm in thickness accordingto a specific embodiment. In another example, the indium layer can bedeposited overlying the copper layer using an electro-plating process,or others dependent on specific embodiment.

FIGS. 1 through 4 illustrate a method of forming a multilayeredstructure 150 comprising copper and indium on a substrate for a thinfilm photovoltaic device according to an embodiment of the presentinvention. In a specific embodiment, copper layer 130 and indium layer140 are provided in a certain stoichiometry to allow for a Cu-richmaterial with an atomic ratio of Cu:In greater than 1 for themultilayered structure 150. For example, the atomic ratio Cu:In can bein a range from about 1.2:1 to about 2.0:1 or larger depending upon thespecific embodiment. In an implementation, the atomic ratio of Cu:In isbetween 1.35:1 and 1.60:1. In another implementation, the atomic ratioof Cu:In is selected to be about 1.55:1. In a preferred embodiment, theatomic ratio Cu:In is provided such that Cu is limiting, which consumesessentially all of the indium species, in the resulting structure. In aspecific embodiment, indium layer 140 is provided to cause substantiallyno change in the copper layer 130 formed until further processing. Inanother embodiment, indium layer 140 can be first deposited overlyingthe electrode layer followed by deposition of the copper layer 130overlying the indium layer. Of course there can be other variations,modifications, and alternatives.

As shown in FIG. 5, multilayered structure 150 is subjected to a thermaltreatment process 200. In a specific embodiment, the thermal treatmentprocess is provided in an environment containing at least a sulfurbearing species 210. The thermal treatment process is performed at anadequate pressure and temperature. In a specific embodiment, the thermaltreatment process is provided at a temperature ranging from about 400Degrees Celsius to about 600 Degrees Celsius. In certain embodiment, thethermal treatment process can be a rapid thermal process provided at thetemperature range for about three to fifteen minutes. In one example,the sulfur bearing species is in a fluid phase. As an example, thesulfur bearing species can be provided in a solution, which hasdissolved Na₂S, CS₂, (NH₄)₂S, thiosulfate, among others. In anotherexample, the sulfur bearing species 210 is gas phase hydrogen sulfide.In other embodiments, the sulfur bearing species can be provided in asolid phase. As merely an example, elemental sulfur can be heated andallowed to vaporize into a gas phase, e.g., as S_(n). In a specificembodiment, the gas phase sulfur is allowed to react to theindium/copper layers. In other embodiments, combinations of sulfurspecies can be used. Of course, the thermal treatment process 200includes certain predetermined ramp-up and ramp down time and ramp-upand ramp-down rate. For example, the thermal treatment process is arapid thermal annealing process. In a specific embodiment, the hydrogensulfide gas is provided through one or more entry valves with flow ratecontrols into the process chamber. The hydrogen sulfide gas pressure inthe chamber may be controlled by one or more pumping systems or others,depending on the embodiment. Of course, there can be other variations,modifications, and alternatives.

In a specific embodiment, the sulfur bearing species can be provided asa layer material overlying the indium and copper layers or copper andindium layers. In a specific embodiment, the sulfur bearing species isprovided as a thin layer or as a patterned layer. Depending upon theembodiment, the sulfur bearing species can be provided as a slurry, apowder, a solid material, a gas, a paste, or other suitable form. Ofcourse, there can be other variations, modifications, and alternatives.

Referring to the FIG. 5, the thermal treatment process 200 causes areaction between copper indium material within the multilayeredstructure 150 and the sulfur bearing species 210, thereby forming alayer of copper indium disulfide material (or a copper indium disulfidethin film) 220. In one example, the copper indium disulfide material orcopper indium disulfide thin film 220 is formed by incorporating sulfurions/atoms stripped or decomposed from the sulfur bearing species intothe multilayered structure 150 with indium atoms and copper atomsmutually diffused therein. In an embodiment, the thermal treatmentprocess 200 results in a formation of a cap layer 221 overlying thetransformed copper indium disulfide material 220. The cap layer containsa thickness of substantially copper sulfide material but substantiallyfree of indium atoms. The cap layer includes a surface region 225. In aspecific embodiment, the formation of this cap layer is under a Cu-richconditions for the Cu—In bearing multilayered structure 150. Dependingon the embodiment, the thickness of the copper sulfide material 221 ison an order of about five to ten nanometers and greater based onoriginal multilayered structure 150 with indium layer 140 overlyingcopper layer 130. Of course, there can be other variations,modifications, and alternatives.

FIG. 6 is a schematic diagram illustrating a process of the method forforming a thin film photovoltaic device according to an embodiment ofthe present invention. The diagram is merely an example, which shouldnot unduly limit the claims herein. One skilled in the art wouldrecognize other variations, modifications, and alternatives. As shown inFIG. 6, a dip process 300 is performed to the copper sulfide material221 that covers the copper indium disulfide thin film 220. Inparticular, the dip process is performed by exposing the surface region225 to a solution of potassium cyanide 310 in a specific embodiment. Ina specific embodiment, the solution of potassium cyanide has aconcentration of about 1 weight % to about 10 weight % according to aspecific embodiment. The solution of potassium cyanide acts as anetchant that is capable of selectively removing copper sulfide material221 from the surface region of the copper indium disulfide material. Theetching process starts from the exposed surface region 225 and down tothe thickness of the copper sulfide material 221 and substantiallystopped at the interface between the copper sulfide material 221 andcopper indium disulfide material 220. As a result the copper sulfide caplayer 221 is selectively removed by the etching process to exposesurface region 228 of the copper indium disulfide thin film materialaccording to a specific embodiment. In a preferred embodiment, the etchselectivity is about 1:100 or more between copper sulfide and copperindium disulfide material. In other embodiments, other selective etchingspecies can be used. In a specific embodiment, the etching species canbe hydrogen peroxide. In certain embodiments, techniques includingelectro-chemical etching, plasma etching, sputter-etching, or anycombination of these may be used. In a specific embodiment, the coppersulfide material can be mechanically removed, chemically removed,electrically removed, or any combination of these, and others. In aspecific embodiment, an absorber layer made of copper indium disulfidecan have a thickness of about 1 to 10 microns, but can be others. Ofcourse, there can be other variations, modifications, and alternatives.

As shown in FIG. 7, the method further process the copper indiumdisulfide material to form a p-type copper indium disulfide film 320 ina specific embodiment. In certain embodiments, the as-formed copperindium disulfide material may have a desirable p-type semiconductingcharacteristic. In a specific embodiment, copper indium disulfidematerial 220 is subjected to a doping process to adjust p-type impurityconcentration therein for the purpose of optimizing I-V characteristicof the high efficiency thin film photovoltaic devices. In an example,aluminum species are allowed to mix into the copper indium disulfidematerial 220. In another example, the copper indium disulfide material220 is mixed with a copper indium aluminum disulfide material. Ofcourse, there can be other variations, modifications, and alternatives.

Subsequently, a window layer 310 is formed overlying the p-type copperindium disulfide material 320. The window layer can be selected from agroup consisting of a cadmium sulfide (CdS), a zinc sulfide (ZnS), zincselenium (ZnSe), zinc oxide (ZnO), zinc magnesium oxide (ZnMgO), orothers. In certain embodiments, these materials may be doped with one ormore suitable impurities to form an n′ type semiconductor material. Thewindow layer and the absorber layer forms a PN junction associated witha photovoltaic cell. The window layer, is heavily doped to form an⁺-type semiconductor layer in a preferred embodiment. In one example,indium species are used as the doping material to cause formation of then⁺-type characteristic associated with the window layer 310. In anotherexample, the doping process is performed under suitable conditions. In aspecific embodiment, the window layer can use an aluminum doped ZnOmaterial. The aluminum doped ZnO material can range from about 200 nm toabout 500 nanometers in a specific embodiment. Of course, there can beother variations, modifications, and alternative

Referring to FIG. 8, the method forms a conductive layer 330 overlying aportion of a first surface region of the window layer 310. Theconductive layer forms a top electrode layer for the photovoltaicdevice. In one embodiment, the conductive layer 330 is a transparentconductive oxide (TCO). For example, the TCO can be selected from agroup consisting of In₂O₃:Sn (ITO), ZnO:Al (AZO), SnO₂:F (TFO), and thelike, but can be others. In another embodiment, the TCO layer isprovided in a certain predetermined pattern to maximize the fill factorand conversion efficiency of the photovoltaic device. In a specificembodiment, the TCO can also function as a window layer, whichessentially eliminates a separate window layer. Of course there can beother variations, modifications, and alternatives.

In a preferred embodiment, the present method maintains an interfaceregion between the electrode layer and the copper indium disulfidematerial substantially free from a metal disulfide layer havingdifferent semiconductor characteristics from the copper indium disulfidematerial. Depending upon the type of electrode material, the metaldisulfide layer is selected from molybdenum disulfide layer or the like.In a specific embodiment, the interface region is characterized by asurface morphology substantially capable of preventing any formation ofthe metal disulfide layer, which is characterized by a thickness ofabout 5 nanometers to about 10 nanometers. In a preferred embodiment,the present method includes a thermal process during at least themaintaining process or a portion of the maintaining process of at least300 Degrees Celsius and greater to prevent any formation of the metaldisulfide layer, which can be a molybdenum disulfide or like layer. Ofcourse, there can be other variations, modifications, and alternatives.

In a specific embodiment, the present invention provides a method forforming a thin film photovoltaic device, which is outlined below.

1. Start;

2. Provide a transparent substrate comprising a surface region;

3. Form a first electrode layer overlying the surface region;

4. Form a copper layer overlying the first electrode layer;

5. Form an indium layer overlying the copper layer to form amulti-layered structure (alternatively indium is formed first or amultiple layers are sandwiched together);

6. Subject at least the multi-layered structure to a thermal treatmentprocess in an environment containing a sulfur bearing species;

7. Form a bulk copper indium disulfide material from at least thetreatment process of the multi-layered structure, the copper indiumdisulfide material comprising a copper-to-indium atomic ratio rangingfrom about 1.2:1 to about 2:1 or 1.35:1 to about 1.60:1 (or preferablyand alternatively from about 0.99:1 or 0.95:1 and less) and a thicknessof substantially copper sulfide material having a copper sulfide surfaceregion;

8. Remove the thickness of the copper sulfide material to expose asurface region having a copper poor surface comprising a copper toindium atomic ratio of less than about 0.95:1 or 0.99:1;

9. Subject the copper poor surface to a sodium species to convert thecopper poor surface from an n-type characteristic to a p-typecharacteristic;

10. Preferably, subject the bulk copper indium disulfide material havingthe copper-to-indium atomic ratio of 0.99 or 0.95:1 and less to a sodiumspecies to convert the copper poor material from an n-typecharacteristic to a p-type characteristic;

11. Subject the copper poor surface and the bulk copper indium disulfidematerial to a treatment process during a time period associated with thesubjecting of the copper poor surface with the sodium species and/orwith the subjecting of the bulk copper indium disulfide material; and

12. Form a window layer overlying the copper indium disulfide material;

13. Form a second electrode layer; and

14. Perform other steps, as desired.

The above sequence of steps provides a method according to an embodimentof the present invention. In a specific embodiment, the presentinvention provides a method and resulting photovoltaic structure freefrom parasitic junction regions in the absorber layer, which impairperformance of the resulting device. Other alternatives can also beprovided where steps are added, one or more steps are removed, or one ormore steps are provided in a different sequence without departing fromthe scope of the claims herein. Details of the present method andstructure can be found throughout the present specification and moreparticularly below.

FIGS. 9-11 are simplified diagrams illustrating a method and structurefor forming a thin film photovoltaic device including sodium speciestreatment according to an embodiment of the present invention. Thesediagrams are merely examples, which should not unduly limit the scope ofthe claims herein. One of ordinary skill in the art would recognizeother variations, modifications, and alternatives. In a specificembodiment, the present method begins with partially completedphotovoltaic device 900. As shown, the device includes a transparentsubstrate 901 comprising a surface region, although other substrates canbe used. The device also includes a first electrode layer 903 overlyingthe surface region. In a specific embodiment, the first electrode layercan be any conductive material including conductive metals, oxides, andsemiconductor or combinations of these, as well as any materialdescribed herein and outside of the present specification.

In a specific embodiment, the photovoltaic device includes achalcopyrite material, which acts as an absorber for the photovoltaicdevice. As shown, the chalcopyrite material can include, among others,copper indium disulfide material, copper indium aluminum disulfide,copper indium gallium disulfide, combinations of these, and others. In aspecific embodiment, the chalcopyrite is copper rich, or alternativelycopper poor and characterized by one or more portions having a copper toindium atomic ratio of 0.99:1 and less or 0.95:1 and less. In apreferred embodiment, the copper indium disulfide material has one ormore copper poor regions, which are preferably compensated using anionic species. Of course, there can be other variations, modifications,and alternatives. In a specific embodiment, the chalcopyrite has a thinlayer of copper sulfide 907, which has been previously described, as mayremain as a residue or fixed material when the bulk material is copperrich. Of course, there can be other variations, modifications, andalternatives.

Referring to FIG. 10, the method selectively removes the thin layer ofcopper sulfide. In a specific embodiment, the thin layer of coppersulfide is removed 909 using a solution of potassium cyanide (KCN) orother suitable technique, e.g., dry etching, plasma etching, sputtering.In a specific embodiment, the method may cause formation of a copperpoor surface region 1001. In a specific embodiment, the copper poorsurface is characterized by a copper to indium atomic ratio of less thanabout 0.95:1 or 0.99:1. In a specific embodiment, the copper poorsurface region is characterized as an n-type material, which forms aparasitic junction with the p-type copper indium disulfide material,which can be rich in copper. The parasitic junction leads to poor orinefficient device performance. Of course, there can be othervariations, modifications, and alternatives.

In a preferred embodiment, the present method subjects the copper poorsurface to an ionic species to convert the copper poor surface from ann-type characteristic to a p-type characteristic, which behaves like anormal copper indium disulfide surface 1101 now, as shown in FIG. 11. Ina preferred embodiment, the method subjects at least one or moreportions of the bulk copper indium disulfide material to one or moreionic species to convert the copper poor region from an n-typecharacteristic to a p-type characteristic. In a preferred embodiment,the ionic species is sodium, which can be derived from NaCl, Na₂S, NaF,or other suitable sodium salts and the like. In a specific embodiment,the subjecting the copper poor surface and/or bulk material includes athermal treatment process during a time period associated with thesubjecting of at least the copper poor surface with the ionic species.In a specific embodiment, the thermal treatment process can range intemperature from about 100 Degrees Celsius to about 500 Degrees Celsius,but can be others. Additionally, the thermal treatment process occursfor a time period ranging from a few minutes to about ten minutes to anhour or so. Of course, there can be other variations, modifications, andalternatives.

In a specific embodiment, the ionic species can be applied using one ormore techniques. These techniques include deposition, sputtering, spincoating, spraying, spray pyrolysis, dipping, electro deposition,painting, ink jet coating, sprinkling, any combination of these, andothers. In some embodiments, the sodium can be diffused from anoverlying material, which can be an electrode layer or molybdenum orother suitable material. Alternatively, sodium can be diffused from apiece of sodium material or the like via a vapor phase. In a specificembodiment, the ionic species such as sodium can be diffused in vaporphase as in the “Siemens” process, but can be others, for short periodsof time. In a specific embodiment, the treatment process passivates thesurface at the heterojunction or the like, which facilitates carrierseparation and transport. Additionally, the present treatment processcan also generate desired conduction band offset, commonly called CBO.Of course, there can be other variations, modifications, andalternatives.

In a specific embodiment, the method includes forming a window layeroverlying the copper indium disulfide material. The method also forms anelectrode layer overlying the window layer. Depending upon theembodiment, the photovoltaic cell can be coupled to a glass ortransparent plate or other suitable member. Alternatively, thephotovoltaic cell can be coupled to another cell, e.g., bottom cell, toform a tandem or multi junction cell. Again, there can be othervariations, modifications, and alternatives.

FIG. 12 is a simplified diagram of an copper indium disulfide materialhaving one or more copper poor regions according to an embodiment of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims herein. One of ordinary skill inthe art would recognize other variations, modifications, andalternatives. As shown, the diagram provides a thin film photovoltaicdevice 1200. The device has a substrate (e.g., transparent) 1201comprising a surface region. Depending upon the embodiment, thesubstrate can be made of any of the materials described herein as wellas out side of the present specification. In a specific embodiment, thedevice has a first electrode layer 1203 overlying the surface region anda chalcopyrite material 1205, which is an absorber, overlying thesurface region. The device also has a copper poor copper indiumdisulfide bulk region 1205 and a chalcopyrite material surface region.In a specific embodiment, the copper poor copper indium disulfide bulkregion having an atomic ratio of Cu:In of about 0.99 and less. In aspecific embodiment, the device has compensating sodium species 1204provided within one or more portions of the copper poor copper indiumdisulfide region to change the copper poor copper indium disulfideregion from an n-type characteristic to a p-type characteristic. Alsoshown is a window layer 1207 overlying the copper indium disulfideregion and a second electrode layer 1209 overlying the window layer. Ofcourse, there can be other variations, modifications, and alternatives.Additionally, any of the elements described herein can be made of any ofthe materials or combination of materials described within the presentspecification and outside of the specification as well.

Although the above has been illustrated according to specificembodiments, there can be other modifications, alternatives, andvariations. Additionally, although the above has been described in termsof copper indium disulfide, other like materials such as copper indiumgallium disulfide, copper indium aluminum disulfide, combinationsthereof, and others can be used. Other materials may include CuGaS₂,CuInSe₂, Cu(InGa)Se₂, Cu(InAl)Se₂, Cu(In,Ga)SSe, combinations of these,and the like. It is understood that the examples and embodimentsdescribed herein are for illustrative purposes only and that variousmodifications or changes in light thereof will be suggested to personsskilled in the art and are to be included within the spirit and purviewof this application and scope of the appended claims.

1. A method for forming a thin film photovoltaic device, the methodcomprising: providing a transparent substrate comprising a surfaceregion; forming a first electrode layer overlying the surface region;forming a copper layer overlying the first electrode layer; forming anindium layer overlying the copper layer to form a multi-layeredstructure; subjecting at least the multi-layered structure to a thermaltreatment process in an environment containing a sulfur bearing species;forming a copper indium disulfide material comprising a copper poorsurface from at least the treatment process of the multi-layeredstructure; subjecting at least a portion of the copper poor surface ofthe copper indium disulfide material to a sodium species; and forming awindow layer overlying the copper indium disulfide material.
 2. Themethod of claim 1 wherein the subjecting of the sodium species isprovided by at least one process selected from spin coating, spraying,spray pyrolysis, pyrolysis, dipping, deposition, sputtering, orelectrolysis.
 3. The method of claim 1 wherein the sodium speciescomprises sodium ions.
 4. The method of claim 1 wherein the copperindium disulfide comprises a thickness of copper sulfide material, thethickness of copper sulfide material being selectively removed using asolution of potassium cyanide.
 5. The method of claim 1 wherein thewindow layer is selected from a group consisting of a cadmium sulfide, azinc sulfide, zinc selinium, zinc oxide, or zinc magnesium oxide.
 6. Themethod of claim 1, wherein the subjecting to a sodium species isperformed during at least a thermal treatment process characterized by atemperature ranging from about 100 Degrees Celsius to about 500 DegreesCelsius.
 7. The method of claim 6 wherein the thermal treatment processis provided in an environment containing at least a sulfur bearingspecies comprising hydrogen sulfide in a fluid phase.
 8. The method ofclaim 1 wherein the forming of the copper layer is provided by asputtering process or plating process.
 9. The method of claim 1 whereinthe sodium species compensates for any missing copper in the copper poorsurface.
 10. The method of claim 1 wherein the forming of the indiumlayer is provided by a sputtering process.
 11. The method of claim 1wherein the forming of the indium layer is provided by a platingprocess.
 12. The method of claim 1 wherein the copper indium disulfidematerial comprises a p-type semiconductor characteristic.
 13. The methodof claim 1 wherein the window layer comprises an n⁺-type semiconductorcharacteristic.
 14. The method of claim 1 further comprising introducingan indium species in the window layer to cause formation of an n⁺-typesemiconductor characteristic.
 15. The method of claim 1 wherein thecopper indium disulfide material is mixed with a copper indium aluminumdisulfide or copper indium gallium disulfide.
 16. A method for forming athin film photovoltaic device, the method comprising: providing atransparent substrate comprising a surface region; forming a firstelectrode layer overlying the surface region; forming a copper indiummaterial by at least sputtering a target comprising an indium coppermaterial; subjecting the copper indium material to thermal treatmentprocess in an environment containing a sulfur bearing species; forming acopper poor copper indium disulfide material from at least the thermaltreatment process of the copper indium material; compensating for thelack of copper in the copper poor copper indium disulfide material usinga sodium species; and forming a window layer overlying the copper indiumdisulfide material.
 17. The method of claim 16 the compensating isprovided by at least one process selected from spin coating, spraying,spray pyrolysis, pyrolysis, dipping, deposition, sputtering, orelectrolysis.
 18. The method of claim 16 wherein the sodium speciescomprises sodium ions.
 19. The method of claim 16 further comprisingsubjecting at least the copper poor copper indium disulfide material toa thermal treatment process characterized by a temperature from about100 Degrees Celsius to about 500 Degrees Celsius.
 20. The method ofclaim 19 wherein the thermal treatment process is provided in anenvironment containing at least a sulfur bearing species comprisinghydrogen sulfide.
 21. The method of claim 16 wherein the window layer isselected from a group consisting of a cadmium sulfide, a zinc sulfide,zinc selenium, zinc oxide, or zinc magnesium oxide.
 22. The method ofclaim 16 further comprising forming a transparent conductive oxideoverlying a portion of the window layer.
 23. The method of claim 16wherein the copper poor copper indium disulfide material aftercompensation has a p-type semiconductor characteristic.
 24. The methodof claim 16 wherein the window layer comprises n⁺-type semiconductorcharacteristic.
 25. The method of claim 16 further comprisingintroducing an indium species in the window layer to cause formation ofan n⁺-type semiconductor characteristic.
 26. A method for forming a thinfilm photovoltaic device, the method comprising: providing a substratecomprising a surface region; forming a first electrode layer overlyingthe surface region; forming a chalcopyrite material overlying theelectrode layer, the chalcopyrite material including a copper poorcopper indium disulfide region; altering a characteristic of the copperpoor copper indium disulfide region using a sodium species; forming awindow layer overlying the chalcopyrite material; and forming a secondelectrode layer overlying the window layer.